#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int i;
	float sum = 0.0;
	for (i = 1; i <= 100; i++)
	{
		if (i % 2 == 1)
			sum = sum + 1.0 / i;
		else
			sum = sum - 1.0 / i;
	}
	printf("%f",sum );
	return 0;
}